1. Field of the Invention
The present invention relates to a valve apparatus such as an electrically operated valve, an electromagnetic valve or the like which is used by being incorporated in a heat pump type cooling and heating system or the like, and more particularly to a valve apparatus provided with a function of a relief valve which can relieve a fluid within a valve chamber in the case that the fluid within the valve chamber comes to a high pressure in a valve closed state.
2. Description of the Conventional Art
Conventionally, as a heat pump type cooling and heating system, there has been known a structure in which two expansion valves are provided for improving an energy saving efficiency or the like, the expansion valve being provided only one normally, in addition to a compressor, an outdoor heat exchanger, an indoor heat exchanger, a four-way switching valve and the like, and check valves are incorporated respectively in two expansion valves in parallel (a structure formed as an expansion valve with check valve) for reducing a pressure loss as much as possible (for example, refer to FIG. 6 of the Japanese Unexamined Patent Publication No. 2010-249246).
Further, there has been recently thought a matter that at least one of two expansion valves with check valve is replaced by an electronically controlled type electrically operated valve (refer to the Japanese Unexamined Patent Publication No. 2009-14056).
FIG. 4 shows an example of a heat pump type cooling and heating system which is provided with an electronically controlled type electrically operated valve serving as the expansion valve with check valve mentioned above. A heat pump type cooling and heating system 100 in an illustrated example is provided with an expansion valve 106 with a check valve 106B corresponding to one of two expansion valves with check valve mentioned above, an electronically controlled type electrically operated valve 10′ serving as another of two expansion valves with check valve mentioned above, a distributor 108, a refrigerant recovering tank 120, and service valves for maintenance (manually operated) 121 and 122, in addition to a compressor 101, a four-way switching valve 102, an outdoor heat exchanger 103 and an indoor heat exchanger 104.
Describing in detail, the electrically operated valve 10′ and the refrigerant recovering tank 120 are arrange in an outdoor side (the outdoor heat exchanger 103 side) which is right side of two service valves 121 and 122 (which are normally in a fully open state), and the expansion valve 106 with the check valve 106B is arranged in an indoor side (the indoor heat exchanger 104 side) which is left side of two service valves 121 and 122. A temperature sensitive type (a mechanical type) structure is used as an expansion valve 106A of the expansion valve 106 with the check valve, and the check valve 106B is arranged in parallel to the expansion valve 106A.
In this cooling and heating system 100, at a time of a cooling operation, a refrigerant which is compressed by the compressor 101 is introduced into the outdoor heat exchanger 103 via (ports a→d of) the four-way switching valve 102 as shown by a solid arrow in the drawing, and is heat exchanged with an ambient air so as to be condensed, and the condensed refrigerant flows into the expansion valve 106 via the distributor 108, the electrically operated valve 10′ (at a maximum opening degree at this time) and the service valve 121, is adiabatically expanded here, thereafter flows into the indoor heat exchanger 104, is heat exchanged with an indoor air in the indoor heat exchanger 104 so as to be evaporated, and cools a room inside. The refrigerant coming out of the indoor heat exchanger 104 is sucked into the compressor 101 via the service valve 122 and (ports b→c of) the four-way switching valve 102.
On the contrary, at a time of a heating operation, the refrigerant which is compressed by the compressor 101 is introduced into the indoor heat exchanger 104 via (ports a→b of) the four-way switching valve 102 and the service valve 122 as shown by a broken arrow in the drawing, and is heat exchanged with the indoor air here so as to be condensed, heats up the room inside, thereafter flows into the electrically operated valve 10′ (regulated its opening degree in correspondence to a cooling temperature at this time) through the check valve 106B (bypass the expansion valve 106A), is depressurized here, is thereafter introduced into the outdoor heat exchanger 103 via the distributor 108, is evaporated here, and is thereafter sucked into the compressor 101 via (ports d →c of) the four-way switching valve 102.
Next, a description will be given of an example of the electronically controlled type electrically operated valve 10′ which is used in the cooling and heating system 100 as mentioned above with reference to FIG. 3. The electrically operated valve 10′ of the illustrated example is provided with a valve shaft 25 which has a lower large diameter portion 25a and an upper small diameter portion 25b and is integrally provided with a valve body portion 24 having a specific shape (two stages of inverted circular truncated cone shapes respectively with predetermined center angles) in a lower end portion of the lower large diameter portion 25a, a valve main body 20 which has a valve chamber 21, a can 40 which is bonded in a sealing manner in its lower end portion to the valve main body 20, a rotor 30 which is arranged in an inner periphery of the can 40 so as to be spaced at a predetermined gap α, a stator 50 which is outward fitted to the can 40 so as to rotationally drive the rotor 30, and a screw feeding mechanism which is arranged between the rotor 30 and the valve main portion 24 and moves the valve body portion 24 close to and away from a valve port 22a by utilizing a rotation of the rotor 30, and is structured such as to regulate a passing flow rate of the refrigerant by changing a lift amount of the valve body portion 24.
The valve chamber 21 of the valve main body 20 is provided with a valve seat 22 formed therein a valve port (an orifice) 22a which the valve body portion 24 comes close to and away from, a first inlet and outlet 11 constructed by a conduit pipe joint is provided in a side portion, and a lower portion of the valve main body 20 is provided with a second inlet and outlet 12 constructed by a conduit pipe joint so as to be connected to the valve port 22a. 
The stator 50 is constructed by a yoke 51, a bobbin 52, stator coils 53 and 53, a resin mold cover 56 and the like, a stepping motor is constructed by the rotor 30 and the stator 50, and an elevation driving mechanism for regulating a lift amount (=a valve opening degree) of the valve body portion 24 with respect to the valve port 22a is constructed by the stepping motor, a screw feeding mechanism and the like. In this case, a lower end portion of the stator 50 is provided with a rotation preventing device 46, and a tubular locking device 47 is firmly attached to a side portion of the valve main body 20 for locking the rotation preventing device 46.
A support ring 36 is integrally connected to the rotor 30, and an upper protruding portion of a lower opened and tubular valve shaft holder 32 which is arranged in an outer periphery of the valve shaft 25 and a guide bush 26 is fixed by caulking to the support ring 36, whereby the rotor 30, the support ring 36 and the valve shaft holder 32 are integrally connected.
The screw feeding mechanism is pressed into and fixed to a fitting hole 42 provided in the valve main body 20 in its lower end portion 26a, and is constructed by a fixed thread portion (a male thread portion) 28 which is formed in an outer periphery of the tubular guide bush 26 to which (the lower large diameter portion 25a of) the valve shaft 25 is inward inserted slidably, and a movable thread portion (a female thread portion) 38 which is formed in an inner periphery of the valve shaft holder 32 and is engaged with the fixed thread portion 28.
Further, an upper small diameter portion 26b of the guide bush 26 is inward inserted to an upper portion of the valve shaft holder 32, and the upper small diameter portion 25b of the valve shaft 25 is inserted to (a through hole formed in) a center of a ceiling portion of the valve shaft holder 32. A push nut 33 is pressed into and fixed to an upper end portion of the upper small diameter portion 25b of the valve shaft 25.
Further, the valve shaft 25 is outward inserted to the upper small diameter portion 25b of the valve shaft 25, and is normally energized downward (in a valve closing direction) by a valve closing spring 34 which is constructed by a compression coil spring installed in a compression manner between the ceiling portion of the valve shaft holder 32 and an upper end terrace surface of the lower large diameter portion 25a in the valve shaft 25. A return spring 35 constructed by a coil spring is provided in an outer periphery of the push nut 33 on the ceiling portion of the valve shaft holder 32.
To the guide bush 26, there is firmly fixed a lower stopper body (a fixing stopper) 27 which constructs one of rotation and downward movement stopper mechanisms for inhibiting a further rotation and downward movement at a time when the rotor 30 is rotated and moved downward to a predetermined valve closing position, and to the valve shaft holder 32, there is firmly fixed an upper stopper body (a movable stopper) 37 which constructs another of the stopper mechanisms.
In this case, the valve closing spring 34 is arranged for obtaining a desired seal pressure in a valve closed state in which the valve body portion 24 seats on the valve port 22a (preventing a leakage), and for reducing an impact at a time when the valve body portion 24 comes into contact with the valve port 22a. 
In the electrically operated valve 10′ structured as mentioned above, the rotor 30 and the valve shaft holder 32 are rotated in one direction with respect to the guide bush 26 which is fixed to the valve main body 20, by supplying an electrifying and exciting pulse to the stator coils 53 and 53 in accordance with a first mode, and on the basis of a screw feeding of the fixed thread portion 28 of the guide bush 26 and the movable thread portion 38 of the valve shaft holder 32, for example, the valve shaft holder 32 moved downward, the valve body portion 24 is pressed to the valve port 22a, and the valve port 22a is closed (a fully closed state).
At a time point when the valve port 22a is closed, the upper stopper body 37 has not come into contact with the lower stopper body 27 yet, and the rotor 30 and the valve shaft holder 32 further rotate and move downward while the valve body portion 24 closes the valve port 22a. In this case, the valve shaft 25 (the valve body portion 24) does not move downward, however, the valve shaft holder 32 moves downward, whereby the valve closing spring 34 is compressed at a predetermined amount. As a result, the valve body 24 is strongly pressed to the valve port 22a, the upper stopper body 37 comes into contact with the lower stopper body 27 on the basis of the rotation and the downward movement of the valve shaft holder 32, and the rotation and the downward movement of the valve shaft holder 32 are forcibly stopped even if the pulse supply with respect to the stator coils 53 and 53 is thereafter carried on.
On the other hand, if the electrifying and exciting pulse is supplied in accordance with a second mode to the stator coils 53 and 53, the rotor 30 and the valve shaft holder 32 are rotated in a reverse direction to that mentioned above with respect to the guide bush 26 which is fixed to the valve main body 20, and the valve shaft holder 32 moves upward this time on the basis of the screw feeding of the fixed thread portion 28 of the guide bush 26 and the movable thread portion 38 of the valve shaft holder 32. In this case, since the valve closing spring 34 is compressed at the predetermined amount as mentioned above, at a time point of starting the rotation and the upward movement of the valve shaft holder 32 (a time point of starting the pulse supply), the valve body portion 24 is not disconnected from the valve port 22a and remains in the valve closed state (a lift amount=0) until the valve closing spring 34 extends at the predetermined amount mentioned above. Further, if the valve shaft holder 32 is further rotated and moved upward after the valve closing spring 34 extends at the predetermined amount, the valve body portion 24 is disconnected from the valve port 22a and the valve port 22a is opened, so that the refrigerant passes through the valve port 22a. In this case, it is possible to optionally and finely regulate the lift amount of the valve body portion 24, in other words, an effective opening area (=a valve opening degree) of the valve port 22a on the basis of an amount of rotation of the rotor 30. Further, since the amount of rotation of the rotor 30 is controlled by a supply pulse number, it is possible to control a flow rate of the refrigerant at a high precision (refer to the Japanese Unexamined Patent Publication No. 2010-249246).
Accordingly, in the case that the electrically operated valve 10′ having the structure mentioned above is incorporated in place of the expansion valve with check valve into the heat pump type cooling and heating system 100, it is set to a maximum opening degree (a maximum lift amount) in such a manner as to reduce the pressure loss as much as possible, at a time when the refrigerant is circulated in one direction (at a time of the cooling operation), and it is set such as to finely control the opening degree (the lift amount) in a specific range which is equal to or less than a predetermined value in such a manner as to carry out a flow rate control, at a time when the refrigerant is circulated in another direction (at a time of the heating operation) (refer to the Japanese Unexamined Patent Publication No. 2009-14056).
In this case, in the heat pump type cooling and heating system 100 provided with the electrically operated valve 10′ as mentioned above, if the refrigerant leaks to the indoor side at a time of the maintenance, all the refrigerant within the system leaks into the room inside, and there is a risk that an oxygenless state is generated. Accordingly, the following operation is carried out at a time of the maintenance.
In other words, at a time of the maintenance, the service valve 121 is closed, the service valve 122 remains in being open, the four-way switching valve 102 is set to the same state (a→d, b→c) as the time of the cooling operation, the electrically operated valve 10′ is set to the fully closed state (no electrifying state), the compressor 101 is started, and the refrigerant is sucked out of the indoor side so as to be discharged to the outdoor side. In accordance with this, the refrigerant pressure within the outdoor side piping becomes large, the refrigerant pressure (the high pressure) acts on the valve shaft 25 (the valve body portion 24) from the second inlet and outlet 12 of the electrically operated valve 10′, the valve shaft 25 (the valve body portion 24) is pushed up against the energizing force of the valve closing spring 34, and a part of the refrigerant is recovered into the refrigerant recovering tank 120 through the second inlet and outlet 12 of the electrically operated valve 10′→the valve port 22a→the valve chamber 21→the first inlet and outlet 11 (at this time, the electrically operated valve 10′ works like a relief valve). If approximately all the refrigerant is collected in the outdoor side (between the service valves 122 and 121) including the tank 120, a desired maintenance work is carried out by closing the service valve 122 and stopping the compressor 101.